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Bats use sonar to navigate and hunt. Many have been killed by wind turbines, however, which their sonar doesn't seem to recognize as a danger. Surprisingly, radar signals could help keep bats away from wind turbines, scientists have now discovered.

Although wind power promises to be a clean source of energy, some researchers have raised concerns that wind turbines inadvertently kill bats and other flying creatures. For instance, in 2004, over the course of six weeks, roughly 1,764 and 2,900 bats were killed at two wind farms in Pennsylvania and West Virginia, respectively. The bats might not be killed by the wind turbine blades directly, but instead by the sudden drop in air pressure the swinging rotors induce, which in turn cause their lungs to over-expand and burst surrounding blood vessels.

The researchers discovered that radar helped keep bats away, reducing bat activity by 30 to 40 percent. The radar did not keep insects away, which suggests that however the radar works as a deterrent, it does so by influencing the bats directly and not just their food.

Radar signals can lead to small but rapid spikes of heat in the head that generate sound waves, which in turn stimulate the ear.

"A bat's hearing is much more sensitive than ours," Racey noted. "It may be so sensitive that even a tiny amount of sound caused by electromagnetic radiation is enough to drive them out of there."

Future research can design a radar system optimized at deterring bats.

So how does radar keep bats away? The researchers explained that a great deal of research suggests that people can actually hear radar pulses.

"This was noticed when radar arrays first started up during World War II," Racey said. "A portion of radar operators said they heard clicks in their ears when they were switched on.""